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<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
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  <body>
    <script>
      var num = 1000 * 60 * 60 * 24 * 7;

      function sevenAfter(num) {
        var nowDate = +new Date(),
            newDate;

        newDate = nowDate + num;

        var seven = new Date(newDate);
        return seven;
      }

      // 方法一
      new Date.setDate(new Date().getDate + 7);
      // 方法二
      new Date(Date.now() + 1000*60*60*24*7);
    </script>
  </body>
</html>
